#define _CRT_SECURE_NO_WARNINGS 1
#include <queue>
using namespace std;
  struct TreeNode {
      int val;
      TreeNode *left;
      TreeNode *right;
      TreeNode() : val(0), left(nullptr), right(nullptr) {}
      TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
      TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
  };
 
class Solution {
public:
    int minDepth(TreeNode* root)
    {
        if (root == nullptr) return 0;
        queue<TreeNode*> q;
        q.push(root);
        int count = 0;
        while (!q.empty())
        {
            int cnt = q.size();
            ++count;
            while (cnt--)
            {
                auto cur = q.front();
                if (cur->left == nullptr && cur->right == nullptr) return count;
                q.pop();
                if (cur->left) q.push(cur->left);
                if (cur->right) q.push(cur->right);
            }
        }
        return count;
    }
};